The ballast resistor in my coupe measures 1.0 ohms. Nothing I can find online is rated at 1.0 ohms. I can find some for 0.8, 1.4, 1.5, 1.6...etc. I just want a spare for when/if this one craps out. Any thoughts? Is 0.8 "close enough?" Thanks. D
IMO, yes. I don't know what kind of meter you have, but lots of digital versions aren't very accurate at low levels.
Geez, I always thought a ballast resistor was just a ballast resistor...fry one, and just go to NAPA and get another one. I guess I wasn't aware that they had any kind of different ratings...of course that was the old points distributor days. Maybe it makes a difference with electronic ignitions.
I don’t know, either, Jack! There’s kind of a divide on whether or not I should even be using a ballast resistor with my Pertronix Ignitor. It seemed like a lot of the experts were steering me toward the fact that it’s been running for a long time just fine with the resistor in place, and a thread from 2009 that I pulled up from here Sort of confirmed that thought- from Hot Rod Don, who apparently is a Pertronix guru. I figure I’d like to keep it the same, but I also don’t wan to get caught stranded. I had an Ignitor a long time ago that I am sure I removed the resistor on and it didn’t last me very long, so I’ll try it this way now.
BTW- I have a 0.8 and a 1.2 on the way…I figure I can test them with my meter and figure out which is closer.
Yeah, I think we need some experts here. When I first built my old '32 (302 Ford) I was running a points distributor with a ballast . Later on, I switched to a Mallory Unilite but was too lazy to rewire...and left the ballast resistor in the ignition circuit...worked fine...ran it for 12 years that way.
With a problem like that, if you can get a 2 ohm resistor, get two, and hook them in parallel for 1 ohm of resistance. Roger
I’ve used the stock resistor on the Pertronix II for 8 years in my car. If it fails I’ll jumper around it since so many don’t use one at all. I’ll replace it ASAP. The tech at Pertronix said either way but the spark would not be quite as hot with one installed. My thinking said the coil would run cooler.
I don't think it makes any difference. Anything between 1 & 2 ohm should work fine. the term 'ballast' refers to its function of stabilizing the system, adjusting the voltage and current going to the coil. A ballast resistor actually changes resistance in reaction to changes in current/voltage/temperature so its nominal resistance is a ballpark rating. All 12V systems need the same amount of regulation so any ballast resistor should work.
Hope this was a joke! That's not the way resistors in parallel work. Paralleling resistors raises the current capacity of the circuit, but has no effect on resistance.
Actually that’s exactly how it works. Every time you add a branch in parallel you decrease circuit resistance hence the increased amperage flow…pesky ohms law.
When I first started looking for a replacement for points because of failing condensers the only thing I found written down about Pertronix at the time was failing coils. Many said they were very hot before failure. I decided to use their coil which was/is an option and use the resistor. I’m a retired power plant electrician of 45 years and understand electrical parts. Just made sense to me. If there is a performance advantage in daily driving I probably could not detect it.
The problem with a ballast resistor in a Pertronix system lies in making sure the module has a full 12 volts, in other words you shouldn't run the wire from the ballast resistor to the Pertronix module. I will try to attach a diagram, the second illustration shows the wire from the resistor going to the coil but a wire bypassing the resistor going to the module. Ballast resistors change resistance with heat, the hotter they get the more resistance they have. When the engine idles the points are closed for a longer period of time then when the engine is at higher RPM, the resistor sees current flow for a longer period and heats up limiting some current flow to keep the points (or module) from damage. While cranking the engine is at very low rpm and AND reduced battery voltage, if the voltage drops below 10.5 volts to the module it can and will get intermittent signal issues and possibly a no start. The ballast resistor is in series with the coil and the resistance of the resistor + the coil resistance = the total resistance and the current flow the points or module see is based on this total resistance. As long as this current flow isn't too high the points or module are happy, if the current exceeds the capacity things go upside down fast. And 1971BB427, resistors in parallel DO reduce resistance, resistors in series increase resistance.
Since we are only addressing vehicles which were originally points I have the Flame Thrower coil wired like your second wiring diagram with one difference. The stock wiring for the car has a wire from the starter solenoid to the (+) side of the coil with assures 12+ volts during startup. Autos with resistor wire from the ignition switch are the ones needing extra work to assure continuous 12v to the coil as they usually have a wire also from the starter solenoid for starting but rely on the resistor wire for running.
You are right about the second wire from the solenoid to deliver full power during cranking. The point I was trying to make is the Pertronix module wants full battery voltage ALL the time, not just during cranking and the ballast resistor ohm value is usually matched to the coil resistance value so the total resistance of both is equal to what the points or module can handle. The windings in the coil vary due to inductance, not just resistance so the manufacture of the module or whatever device is going to fire the coil has tested the circuit for optimal performance. That is why there are so many different coils and resistors out there. If Pertronix, MSD, Mallory, Chevrolet, whoever recommends a certain coil resistance or resistance value for a resistor there is a lot of engineering and testing that happens before they make that recommendation. The very start of this post was a resistor value of 1.0 ohms, I wouldn't think 1.2 ohms would be an issue due to the higher resistance reducing current flow slightly. I would be more worried if I went to a 0.8 ohm because of the increased current flow. Both may work fine in his application but neither one may be optimal based on the coil being used. Sorry for the short story long.
Pertronix II module may receive full voltage as shown in the middle diagram but my purchased Flame Thrower coil receives ballast resistor voltage and performs flawlessly. No sweat with your explanation.
Is there a way to tell if a coil has a ballast resistor built in the coil. When I run an external resistor with my Mallory Unilite, it will start but immediately die. When run with 12v direct to coil, it runs fine. It seems to have too low voltage to power the coil thru the resistor. I'm currently running a Flame Thrower Ignition Coil 1.4 ohm 1.5 OHM Ballast Resistor
Do you have continuity through the resistor? Might be bad. If my memory serves me- the symptom I had was that the Ford starter solenoid allows it to start but not stay running. I lost the entire 12v circuit to my coil so my fix was to run a new fused 12v between my switch and resistor.
Sound more like an external electrical problem. The ballast resistor and coil get their feed from different circuits.
GMC Bubba suggested I run a ballast resistor with a Petronix. My coil was so hot you couldn’t touch it. It worked great for awhile. Till I probably left the key on.
I remember installing a capacitive discharge unit in the 1960s and the instructions said to remove the ballast resistor. I think I would trust an answer to your particular question that came from Petronix more than an answer from a discussion group.
In a word, no. There's confusion over just why a ballast resistor is used. There are several reasons, but those have been muddied by misleading advertising of some products. First, there's no such thing as a '6V' and '12V' coil, there's merely coils with different internal resistance. Typically, an advertised '12V' coil will have a 2.5-3.5 Ohm primary resistance, a '6V' will be half of that. A '12V' coil may have an internal resistor but is more likely to have been simply wound differently to produce the higher primary resistance. So all you're really looking for is the higher primary resistance, how it's achieved doesn't matter for our purposes. When Detroit made the switch from 6 to 12 volts, they didn't change the ignition coils to any great degree. The increased voltage and current due to the low internal coil resistance would produce a hotter spark, making the ignition more efficient. Two problems reared their heads unfortunately; first, the higher voltage causes more arcing when the points switch the ignition current, substantially reducing point life. Second, coil overheating became a problem, and I'll cover this more further down. Installing a resistor in series with the coil primary to drop the voltage back to 6V reduced these effects enough to restore longevity and reliability in 'normal' driving conditions. But the OEMs noticed that the increased voltage markedly improved ignition starting performance, so a ballast resistor 'bypass' was installed that was only active when the starter was engaged. Wiring is pretty basic. You need a power wire from the 'run' position on your ignition switch to one end of the resistor, the other end of the resistor connects to the + terminal of your coil. Wire the bypass one of two ways; if you're using a Ford starter solenoid with the 'S' (start) and 'I' (ignition) terminals, connect the 'I' terminal to the distributor end of the ballast resistor. This terminal is only 'hot' when the starter is engaged. No solenoid? Then run a wire from the 'start' terminal at the ignition switch to the distributor end of the resistor. When you get to electronic ignitions, it can get complicated. Some require the ballast resistor, some won't if you use their 'special' coil (usually, just a coil with a higher primary resistance), some won't need the ballast resistor at all. Generally speaking, the less-expensive 'under-the-cap' conversions and older electronic conversion distributors will require the resistor as the electronic components can't withstand the higher current for more than brief periods without failing. The 'better' units will have an auto-shutoff feature to prevent damage. But the top-of-the-line units will have all that plus current-limiting circuitry and/or dwell control. The aftermarket 'box' ignitions are generally of this type. These circuits control coil overheating by limiting the 'on' time to the coil (dwell control) or limiting current by RPM. Coil overheating is caused by excessive 'on' time at lower RPMs, such as while idling or at lower driving speeds. What is happening is it takes a certain amount of time to 'charge' the coil (build to maximum magnetic saturation). Once the maximum saturation is reached, any additional power put into the coil sees it as a dead short and produces heat. As RPM climbs, the 'on' time goes down. Whatever electronic ignition you use, pay attention to their recommendations as to coil selection if one is made. I personally prefer the MSD box ignitions as you can run almost any coil, including a OEM unit, and still get good performance while maintaining stock-style appearance if you hide the box.